Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a technique for improving its resistance to electrostatic discharge (ESD).
Description of the Background Art
Traditional liquid crystal displays (LCDs) have typically included a front frame that covers four sides of the front surface of a liquid crystal panel. In recent years, the LCD having a structure (no front-frame structure) that does not include a front frame is becoming increasingly common on grounds of design and mechanism.
The front frame included in the LCD is fixed to the liquid crystal panel to cover a driver IC (including a source driver IC that outputs a display signal and a gate driver IC that outputs a scan signal) that drives each pixel of the liquid crystal panel such that the drive IC can be protected from electrostatic discharge (ESD). Thus, the LCD having no front-frame structure includes, in place of the front frame, a conductive tape (hereinafter referred to as the “shielding tape”) bonded to the liquid crystal panel in order to protect the driver IC from ESD. The shielding tape also protects, in many cases, the electronic components, such as peripheral circuits (including a bypasscapacitor) of the driver IC, a control circuit, and a power supply circuit if these electronic components are mounted on a FPC that is connected with the driver IC.
The shielding tape is usually bonded only to the side of the liquid crystal panel with the driver IC located thereon. When a side with no shielding tape bonded thereto is applied with ESD, ESD noise enters common potential (VCOM) wiring located on the outer periphery portion of the liquid crystal panel due to the absence of discharge path for ESD. Consequently, the given standard requirements cannot be met in some cases. To solve the problem, additional shielding tapes are bonded to the sides with no driver IC mounted thereon.
For example, as disclosed in Japanese Patent Application Laid-Open No. 2001-100233, the thin-film transistor (TFT) array substrate of the liquid crystal panel has a discharge path on each side thereof by including wiring (ground wiring) that is connected with a ground potential (GND) and extends along the outer periphery portion thereof.
If the shielding tapes are bonded to all sides of the liquid crystal panel in the LCD having no front-frame structure, the discharge paths for ESD can be secured on all sides of the liquid crystal panel. In terms of accurate positioning of the shielding tapes to be bonded, the shielding tapes should be bonded to each side one by one, which causes an increase in manufacturing cost. In addition, an increase in the number of shielding tapes to be bonded may reduce the yields because the shielding tapes are more likely to fall off.
ESD may cause problems for the LCD equipped with a front frame that has weak connection with the ground potential (GND connection) (has insufficient discharge paths provided thereto) and for applications (such as, an application used for an amusement game machine) in which the front frame itself does not have the GND connection. Similarly, ESD may cause problems in a case where the liquid crystal panels of the LCDs equipped with a front frame are diverted to those of the LCDs having no front-frame structure (in other words, in the case that the liquid crystal panels of the LCDs equipped with a front frame and the liquid crystal panels of the LCDs having no front-frame structure are standardized).
As disclosed in Japanese Patent Application Laid-Open No. 2001-100233, a discharge path for ESD is formed of the ground wiring extending on the outer periphery portion of the liquid crystal panel, so that the number of shielding tapes can be reduced. However, the applied ESD directly enters the driver IC if the discharge path for ESD is formed of the ground wiring that is connected to the driver IC. This possibly causes a display failure.
As for the liquid crystal panel employing the mode in which the liquid crystals are driven by the transverse electric field (transverse electric field mode), such as the in-plane switching (IPS) mode (“IPS” is a registered trade mark), with a view toward improving the image quality, a transparent conductive film (hereinafter referred to as the “CF transparent conductive film”) made of, for example, indium tin oxide (ITO) is disposed on the surface of a color filter (CF) substrate and is connected with the ground wiring on the TFT array substrate. Such a configuration is employed because the potential change of the color filter substrate causes the display to deteriorate (causes the screen to appear greenish).
In many cases, the CF transparent conductive film and the ground wiring are connected to each other through a conductive tape made of, for example, aluminum or through conductive paste such as silver paste. To conduct a check (hereinafter referred to as the “CF ground check”) on whether the CF transparent conductive film and the ground wiring are properly connected to each other, checking wiring (CF ground checking wiring) that is connected to the CF transparent conductive film is disposed, independently of the ground wiring, on the TFT array substrate and the continuity between the CF ground checking wiring and the ground wiring is tested (the resistance value is measured).